I am in the process of building a 1:20 Lotus 107B. I think it qualifies as one of those. And did a D2 DTM merc a while ago, that surely qualifies!
My method follows - and as allways you'll have to see whether it works for you. Insert disclaimer and all!
For Tamiya decals I mostly tend to go very very hot water with a drop of dishwashing liquid. (Once again, TEST! I've had some very thin ones that did not like the warm water all that much!) 10-15 sec's in there, then onto something soft that will absorb some of the water whilst you add a drop or so of that same water onto the place where you want to apply the decal - helps with moving it around to get the perfect spot.
Then I slide it in place - most often I hold it over the model in the correct place and pull the backing paper from underneath it. Slide it around till it sits perfectly. I then apply microsol, the red bottle. (TEST!!! - but I've not had issues) If you're unfamiliar with it - don't get scared about the initial crumpling of the decal - part of the process, it smooths out great! Do not touch it in the crumpled stage, however! You will spoil your day. Leave it alone till dry. If there are any air bubbles, cut the decal with a very sharp modeling knife where and as needed and apply some more microsol to re-melt that spot.
Importantly, I keep it simple and I do it early. I do one decal, unless there's a bit of a jigsaw of decals, to try to avoid touching it after applying microsol. If there's a jigsaw, I do them together, then microsol all together. By doing it early I mean that I am doing this whilst busy with the 1st steps on the kit, such as building the engine. That way you don't get in a rush to try to finish it.
If you clearcoat, I advise you clearcoat between "layers" of decals. With the 107B I have a huge base colour decal scheme, to be followed at places with sponsor decals on top of them. Microsol will attach the bottom decal (again) as well, so if you inadvertendly moved the top decal whilst applying microsol, you may have a problem.
Very importantly. These decals are usually designed very well. The task at hand may seem near-impossible initially, but just relax and do it slowly. It is never as bad as it seems!
I've heard of some guys using hair driers to help with complex curves, I've never done it personally. Maybe somebody can help you with that technique as well.
Good luck and keep us posted!